When the meteor that Avi Loeb, director of the Institute for Theory and Computation at Harvard University calls IM1 streaked across the sky on 8 January 2014, it was nothing special.
Yes, at half a meter in diameter, it was big enough to put on a nice show for people on the ground, ending in a rapid series of explosions high in the atmosphere.
“There were some reports of flashes in the sky, and there was probably a boom, although I’ve never heard anyone say that,” says Loeb’s colleague, Rob McCallum of Cambridge, Massachusetts.
Normally, that would have been the end of the story. But IM1 means ‘interstellar meteor 1’ and in a pre-print study posted this week on ArXiv, a team led by Loeb and McCallum, which retrieved tiny iron spherules condensed from molten metal that rained down after the asteroid exploded, concluded the asteroid hadn’t come from our own asteroid belt. It came from interstellar space.
Not that this is the first time humans have encountered an extrasolar object. In 2006, NASA’s Stardust mission, whose primary task was to sample the tail of a comet, also scooped up a few grains of dust that appeared to have come from outside our own Solar System. Then in 2017, we were visited by an extrasolar asteroid or burned-out comet called ‘Oumuamua, followed by a rogue comet called Borisovin 2019.
“This one would be the third [interstellar asteroid],” says Humberto Campins, a planetary scientist at the University of Central Florida, Orlando, who was not part of the study team. But there’s a difference between IM1 and ‘Oumuamua and Borisov. This time, Campins says, “we actually have samples.”
Adds Loeb: “It’s the first time humans put their hands on materials that came from a larger object – in this case more than half a meter in diameter – that came from outside the Solar System. That’s never happened before.”
Half-meter asteroid impacts aren’t common, but neither are they super rare. The explosion from this one was big enough to be detected by orbiting satellites, but it languished under the obscure designation CNEOS 2014-01-08 for several years until Loeb and the U.S. Department of Defense began taking a deeper look.
“It’s the first time humans put their hands on materials that came from a larger object.”Avi Loeb
The first discovery was that it had hit Earth’s atmosphere at a speed of 45 km/s – fast enough that the US Space Command concluded there was a 99.999% likelihood it had come from interstellar space.
The data also showed that it plunged unusually deeply into the Earth’s atmosphere before exploding, indicating that it was probably dense enough to be a likely source of iron spherules.
Better yet, the scientists were able to determine it had exploded over the ocean, 84 km north of Manus Island in Papua New Guinea, somewhere in a narrow band 11 km long and 1 km wide.
There was just one problem. The seabed in that area is 2,000 meters deep.
Undeterred, Loeb teamed up with McCallum, who leads expeditions through his company EYOS, got funding from entrepreneur-philanthropist Charles Hoskinson, chartered an Australian tug called the Silver Star, and set out for the waters north of Manus Island. There, they deployed a magnetic sled measuring 1×2 m and designed to retrieve iron particles by skimming across the seabed.
Over the course of 2 weeks, they made 26 such trawls, covering approximately 26 hectares of seabed (about eight city blocks) including not only the impact area but two control zones to the north and south of it: important because iron spherules come from many sources. “We wanted to sample control regions because even near the meteor site you know it’s a combination of background particles that exist everywhere, plus the meteor particles,” Loeb says, “so we wanted to know the background.”
Much of what they got was, of course, normal seabed material, such as iron-containing volcanic ash. But from this, Loeb and his summer intern Sophie Bergstrom tweezered out 722 tiny iron spheres, each about 1 mm in size. 57 of these have now been analyzed, and 5 of them, all from the heart of the impact zone, where they are almost certainly from the asteroid, were decidedly unusual.
“We found a completely new class of spherule, never seen before,” Loeb says.
Their most unusual feature, he says, is that they were extremely rich in three elements – beryllium, lanthanum, and uranium – enough so Stein Jacobsen – Loeb’s collaborator who did the analysis – dubbed them BeLaU spherules.
The lanthanum and uranium are 500 times more plentiful than in earthly rocks, indicative of a source very unlike anything in our solar system. But the beryllium, also hundreds of times more plentiful than on Earth, is even more important.
That’s because beryllium, the second-lightest solid material on the periodic table, is produced by a process called spallation, where it is chipped out from the nuclei of heavier elements by the impact of high-energy cosmic rays. “That is a flag of interstellar travel,” Loeb says, because it can’t occur at such a high level in the Solar System, where the solar wind protects us from the bulk of the radiation that causes it.
Even the iron in these spherules is unusual, with isotope ratios unlike anything we know in the Solar System. “It clearly came from outside,” Loeb says.
Campins is impressed. “It’s enough to be excited about,” he says. “My hat’s off to these people. I think this was a meteorite that came from outside the solar system.”
And not just any meteorite. From the elemental composition, he says, it appears to have come from a parent body big enough to have differentiated or separated into inner and outer layers like a [large] asteroid or planet.
It’s enough to be excited about. My hat’s off to these people. I think this was a meteorite that came from outside the solar system.Humberto Campins
Loeb agrees it is most likely a chip off a distant exoplanet or large exo-asteroid. But there’s another possibility, he says. It might be an artifact – someone else’s space junk that somehow found its way here before crashing into Earth. Unlikely? Yes. Impossible? No.
As well as IM1, Loeb believes there is also an IM2 that exploded offshore from Portugal in 2017. That’s two such objects known or suspected to have hit the Earth this century, indicating that they might not be flukes.
“A random detection rate of 1 per decade for meter-sized interstellar objects [hitting Earth] implies that a few million such objects reside within the orbit of the Earth around the Sun at any given time,” Loeb says. And, he notes, “some of them may represent technological space trash from other civilizations”.
Already, Loeb has plans to go to Portugal and see what he can find. But probably not before he goes back to Papua New Guinea to look for larger fragments of IM1.
His work is, of course, controversial, especially because of his interest in the potential connection to the search for extraterrestrial intelligence (Loeb’s latest book on the subject, Interstellar: the Search for Extraterrestrial Life and Our Future in the Stars, was released within a day of his article on IM1 posted to Arxiv.) But that’s part of what McCallum likes about working with him. “I like his style,” McCallum says. “It’s an exploratory style. As a professional expedition leader, that’s what I admire in people.”